I was wondering if anyone knows of any good research on the caffeine levels of each infusion when brewing multiple short infusions of pu'er with a gaiwan.

Some background:

There is a myth that you can decaffeinate black tea by steeping it for 30 seconds before brewing. There is also a myth out there that when brewing with short infusions the caffeine is released slowly, so that each successive cup has more caffeine in it.

The consensus of the research I've seen seems to be that both of these are nonsense. I have seen studies of English-style brewing that suggest that a second 5-minute infusion with the same leaves will have less caffeine than the first but still be far from "decaf," and that the third 5-minute infusion will have almost none, suggesting that the levels do fall, not rise, over time.
But of course I'm not brewing my pu'er for five minutes at a time.

I've seen studies claiming that a 30-second steep will remove 10% of the caffeine and that a one-minute steep will remove 40%, but I don't have access to those primary sources. But nothing is really directly relevant to, say, a series of 15-45 second steepings.

So, has anyone seen any good research on this question, possibly in the Chinese-language scientific literature? If I stretch out my pu'er to six infusions instead of five, how much am I really adding to my daily caffeine intake?

This reference ought to do it, with the following table telling most of the story (for one measured set of brewing parameters--Western style, I think it was--and tea type, but variation would be limited):

We discussed this on Discord a couple of weeks ago (the r/tea unofficial Discord). Water can only hold so much caffeine. Each successive infusion has less caffeine, but with gongfu, since you're adding fresh water each time, you get a nice, complete extraction of caffeine and other solutes from the leaves.